Automatic station



C. E. CAREY AUTOMATIC STATION July 12, 1927. 1,635,574

INVENTOR W|TNESSES:- v

I Char/es E C/ y ATTORNEY July 12, 1927. Q E. CAREY AUTOMATIC STATION Filed April 1924 2 Sheets-Sheet 2 INVENTOR Cgar/es [Cb/" y I I ATTORNEY DQQQ WITNESSES;

Patented Jul ylz, 1927.

UNITED. STATES,

v 1,635,574 PATENT OFFICE;

cnmms E. cannon wrLxmsnone, PENNSYLVANIA, ASSIGNOR T wns'rme HOUSE nmcrmce MANUFACTURING COMPANY, A CORPORATION OEPENNSYL VANIA.

AUTOMATIC STATION;

Application filed April 2, 1924. Serial No. 703,718. I

Another object of my invention is to provide an'electrical translating station having two translating devices and 'two load circuits 15 that shall have means for causing each of the translating, devices to supply energy to only one of the load circuits under predeterminedconditions. a

. .Another object. of my invention is toprovide a translatin'gstation, of the above-indicated character, that shall supply energy to i one load circuit at avoltage determined by conditions-existing in'that circuit and that shall'supply energy to asecond load circuit 25 at 'a voltage determined by condi-tionsexisting therein.

A further object of my invention is to provide means in a station of the above-indicated character, for automaticallyequalizing the voltages of two circuits that are to be connected andfor then automaticallyeffecting such connection. 7 i A A further object of my invention is ,to provide atra'nsla'ting station, of the above-id J di'cated character, that "shall operate with the maximumeconomy possible, at the same time maintainingas high quality ofservice as possible. g r I In the accompanying drawings,"

Figure 1. is a diagrammatic representation of an electrical system' in which my invention is embodied, and

Fig. 2 is a schematic representation'of the same circuits in which like reference nu- 45 merals are applied to like parts throughout.

' Referring to Fig. 1 of the drawings, translating devices 1 and 2 are adapted to "supply energy to load circuits 3 and 4 through bus sections 5 and 6 an'dcircuitinterrupters 7 5 0 and 8, respectively; A portion of the load circuit 4 is shown in broken'lines to indicate that this circuit may extend for a considerable distance fromthe translating station. A circuit interrupter 9 is provided for connecting the two bus sections 5 and 6.

Itis desired that the translating device l circuits is withinthe capacity of the trans latingdevice land while the voltage across the circuit l at substantially the load center thereof is amount of the normal voltage of the circuit; When this volta'ge falls toa predetermined value, however, or when the total load demand of the two load circuits exceeds the capacity of one translating device, it is desired that the translating device 2 shall be connected to the'bus section 6 and that the circuitinterrupter 9 shall be opened to disconnect the two bus sections 5 and 6.

I The translating device l is adapte'dto be connected to the bus section 5 at all times when the station is 11101361116011. This connection effected bythe manually operated circuitintcrrupter 7 'An operating coil 10 of atwo-coil load relay 11 is connectedin series withthe circuit of the translating device 1, between the circuit interrupter 7 and the bus section. The second operating coil 12 of the load relay 11 is similarly connected in series with the circuit of the translating. device 2 between the circuit interrupter 8 and the bus section 6.

The translating device 1 comprises an armature member 13 and a shunt field-magnet winding 14 havingavvariable resistor 15 in series therewith. The portion of the resistor 15 that is connected in circuit with the field-magnet winding 14 is determined by the position of a contact arm 16 that is actuated by a reversible motor 17 through a' substantially the load center thereof; The

operating coil- 26 of the regulating device co-operates with an armature member 28 that is mounted at one end of a lever arm 29.

The lever arm 29 is supported on a pivot 30 and ha mounted on'the opposite end from that on which the armature member 28 is mounted, the piston31 of a dash pot 32.

A the'same end of the leverarm 29 that supports the armature member 28, a bridgwithin a predetermined ing member 33 is mounted that is adapted to engage contact members 34 when the energization of the coil 26 sufiicient to raise the armature member 28 a predetermined distance above its normal position. i bllt 7 ingmember 35. that is mounted on the opposite end of the lever arm 29. is similarl adapted to engage contact members 36 when the cnergization ot' the coil Elli is belovv a predetermined value. such that the armature member 2 permitted to :tall a predetermined distance tron its normal position. it will be understood that by the normal position of the armature member 28 is meant that position corresponding to the energization of the coil 26 at the normal or desired voltage at the load center of the load circuit 3. i

T he operation of the regulating device 2'," is apparent from the foregoing; description of its structure, but it may be described as follows: li hen the'voltzu' across the load circuit 3 at the load center thcr nelov: the normal or desired valutn the energgization of the operat ng coil 26 ot the resrulating device is insutticient to maintain the armature member 28 in its normal posit on. It therefore drops to cause the bridging member to engage the contact members 36. thereby connecting the arnniturc member 22 and the series field-magnet n'indin 23 (it the reversible motor 17 across the bus section The motor 1? is thereupon caused to rotate in such direction that the contact arm 16 is actuated to lessen the amount of the resistance 15 that is connected in circuit with the shunt field-magnet winding ll of the translating device 1.

is the effective portion of the resistor 15 is lessened, the tield strength 01" the translating device 1 is increased until the voltaege generated by the translatinc device is increased to such value that the voltage across the load circuit 3 at the load center thereof again normal. Thereupon the operatinrr coil 26 ot' the rea'ulatine; device is energized suflicientl to cause the b dging menn ber to be actuated out of eng meat with the contact members 36. The circuit e7:- tending through the armature memler and field-magnet Winding 23 of the motor 117 is thus interrupted and operation of the motor is stopped.

lVhen the voltage of the load circuit 3 exceeds the normal or desired value, the operating; coil 26 ot the regulating device 25 is energized to such degree that the armature member 28 causes the bridging member to engage the contact members 3%, thereby connecting the armature member 22 and the series field-magnet Winding 2t of the reve ble motor 17 across the bus section Vi hen the motor 17 is thus energized. the armature member 22 is caused to rotate in the opposite direction to that previously described so that it now actuates the contact: arm 16 in such direction as to increase the effectiveness of the resistor 15.

The tield streu 'th of the translating device 1 is thus lessened to cause the voltage generated by the translating device also to be lessened. ii hen this voltage has decreased to such value that the voltage across the load circuit 3 again oit normal alue, the bait no member 33 ot the regulating device to r permitted to disengage the contact member 3%, thereby de-energizing the motor 1? to stop the operation thereof. The, dash pot Ira; provided for the purpose of damping the action of the regulating device in order to inane this device more stable in its operation.

The translating device 2 is provided with a voltage regulation device 37 that. issimi- .lar to the regulatn device 3 of the trans lating' device 1. The regulating device 37 cooperates with a reversible motor 38 and a contact arm 89 ."o vary the etljectiveness of a hie resistor it) that is connected in series with a shunt held-magnet winding 4 ot the i trans ating device 2 in the same manor the translating device 1. r extend :trom the loadcenter ot the load circuit to the terminals of an operating coil 4-3 at the regulating; de vice 3'? and al o to the terminals of an operating coil -l-loff a voltaeje relaylf). The voltage relay 4:5 is provided with contact members 436 that are connected in parallel relation with contact members 4-7 oil? the load relay 11 and that are adapted to be engaged when the veltagge across the load circuit 4; at the load center thereof is below a prede- CCllllliilGCl value. I

The contact members t? of the load relay ll. are adapted to he engaged when the total load demand on the translating devices 1 and 2 i o t a predetermined value. Tn- :ismuch as the translating device 2 is not now in operation. as the drawings indicate. the load relay ll l'QFfjOIlSlYG only to the load demand on the translating: device 1, and the contact members 47 will be engaged when the load demand on the translating device 1 exceeds the capacity thereot or when such load demand exceeds any other desired predetermined value.

il heu either or both of the contact memhers it and -il-T are engaged, in response to conditions mentioned above,.a circuit exzingr from the bus s ction 5 to the operatcoil l8 oil a transtcr relav L9 is com- 'ontact members 50 oi the. circuit inter- 53 that are engaged when this circuit in its open position. as is now in the opera one coil 4-? oil the reliiv L49 is energrlzed from the bus 5. th s relav e'llects engagement of contact ers 5i, 53, 5t and and disengagement of its contact members I 56,.57fand 58.

Engagement of the contact member-s 52 elfects connection between one terminal of the armature member of: the reversiblemotor 38 and one sideofithebussection 6. Engagementof the contact members 51completes :a circuit for connecting the operating coil .59 of a second transfer relay in parallel relation with the operating coil48 of the transfer relay 49, thereby causing the coil 59 'also'to be energized from thetbus section 5.- \Vhenthe operatingcoil 59 of the transfer relay 60 is energized, this relay effects engagement of its contact members 61, 62 and 63 and disengagement of its contact members 64"and 65. y

When the contactmembers 54 and 55 of the transfer relay 49 are engaged, an operating coil 66 of a voltage balancing'device 67 is connected across'the terminals of thetransla-ting device 2. It will be assumed either that'the translating device 2 iskept in operation Without'load While the circuit interruptcr 8 is open or that it is started in responseto predetermined conditions when it is desired that it be connected to the bus section 6 for supplying'energy' thereto.

The voltagebalancing device67 is provided witha second operating coil 68 that is connected across the bus section 6 and that is differentially disposed with respect to the g coil 66. The balancing device 67 is similar to-the regulating devices25 and 37 except that it is normally balanced and is provided withftwo operating coils instead of one. When the energization of the, coil 66 is greater than that'of' the coil 68, contact members 69 are engaged; when the opposite condition prevails, contact members 70 are engaged and when the two coils are equally energized, contact'members 71 are engaged.

Contact'members' 6901? the balancing device 67 are connected in series with the contactmembers63 of the transfer'relay 60 and a series field-magnet winding 72 of the reversible motor 38. The contact members 7 0 are similarly connected in series with the contact members 62 of they relayGO and a series field-magnet Winding. 73 of the motor 38. Thus, when the operating coil 59 of the transfer ielay 60'is energized,the operation ofthe reversible motor 38 is controlled by the voltagebalancing device 67.

Inasmuch as the coil .68. of" the balancing" operation, which is -'accomplished by .walternate engagement of the contact members 69 and the contact members 70, is similar to that described in detail with respect/to the operation of the regulating device 25.

\Vhen thevoltagebetween the terminals of the translating device 2'hasbeenmade equal to that ofv the bus section:5,'the balancingdevice 67 will'assume the normal position shown in the drawings, whenthe'contact members 7l are engaged. The contact members 71 are connected inseries Withthe contact members 53 of the transferrrelay .49 and an operating coil 74 of a time-delay 'relay 75 across the bus section 5. The time setting of the relay 75is such that it will not efl ect engagement of its contactmembers v76 and 77 until. the voltage'balancing device 67 has come to its balanced position, when'the centactinembers 71. are engaged for. a relatively long interval of time. Withinia predetermined interval of time after this balanced condition occurs, the contact members 76 and 77 ofthe relay 75 are engaged.

W henthe contact members 77 oftherelay 75 are engaged, a circuit "extendingfrom the bus section to an operating coil. 7 80f the circuit interrupter 8, is completed through aresistor 79. The circuit interrupter 8' is thereupon closed to connect'thetranslating device 2to the bussecti on 6 an-dto effect engagen'ient of auxiliarycontact members 80, 81 and 82 and-disengagement of the auxiliar-v contact members5'0. I

The auxiliary contact members 81 so shunt the contact members77 of thetime-delay relay 75 that energization of the operating coil 78 of the circuit interrupter 8 is maintained after the contact members 77 are disengaged. In like manner, the contact members 82 so shunt the contact members 52 of the transfer relay49 as tomaintain-connection between one'terminal'of the armature member of the reversible motor 38andone side of the bus section 6 after the contact members 52 -are disengaged. I

Up to the time when the circuitinterrupter Sis closed, the circuit interrupter'9 is held closed by the energi zation of its operating coil 83that is connected across the bus sec tion 5 through auxiliary contact members 84: of the circuit interrupter 9 and a resistor 85. When the circuit interrupter '8 is closed,

' however, its auxiliary contact members'80 co-operate with the contact members 76 of the relay 75 to short-circuit the operating coil 8301. the circuit interrupter 9, thereby permitting a compression spring86to effect opening of the circuit interrupter 9.

When the auxiliary contact members 50 are disengaged because of .the closing of the circuit interrupter 8, thecircuits extending through the operating coils 4.8 and 59 of the transfer relaysfit) and 60,'respectively, are interruptedtopermit'these relays to return to their de-energized positions. The contact members 53 of the relay 49 being thus disengaged, the circuit extending through the operating coil 7-1 of the time-delay relay 75 is interrupted to permit this relay also to return to its (ls-energized position.

hen the contact members 63 and 64 of the transfer relay are disengaged and the contact members Get and 65 of the same relay are engaged because of the de-energization of the operating coil 59, connection of the series field-magnet windings T2 and 73 of the reversible motor 38 is transferred from the contact members 69 and 70 of the voltage balancing device 67 to contact members 87 and 88 of the voltage regulating device 37.

Thenceforth, the voltage generated by the translating device 2 is controlled by the regulating device 37 co-operating with the reversible motor 38, contact arm 39, variable resistance 40 and shunt lieldanagnet winding 4-1 of the translating device 2, to maintain the voltage of the load circuit 4% at the load center thereof at a predetermined mine. This operation is accomplished by the connection of the operating coil 13 of the regulating device 37 through the pilot wires l2 to the load center of the load circuit 41.

The two bus sections 5 and (i are now disconnected because the circuit interrupter 9 is open, and are individually receiving energy from the translating devices 1 and 2, respectively. This condition of operation has been accomplished, as described in detail above, in response to either an excessive load demand on the translating device 1 or a decrease of voltage of the load circuit 4, at the load center thereof, below a predetermined value.

It is now desired to maintain this condition of operation until the total load demand on the translating devices 1 and 2 has decreased to such value that it is within the capacity of one translating device, and also until the difference in voltage of the two bus sections 5 and 6 has decreased to a predetermined value. When these two conditions occur simultaneously, it is desired that the voltages of the bus sections 5 and 6 shall be equalized, the circuit interrupter 9 closed. to connect the two bus sections, and the circuit interrupter 8 opened to disconnect the translating device 2 from the system. The means for accomplishing this result will now be described.

A differential voltage relay 89, comprising two operating coils 90 and 91 and a pair of contact members 92, is provided for indicating the decrease of difference in voltage between the bus sections 5 and 6 to a predetermined value. When this condition occurs, the energization of the coils 90 and 91 sutiiciently approaches a state of balance to permit the contact members 92 to be engaged. The contact members 92 are connected in series with contact members 93 of the load relay 11, auxiliary contact members 9i of the circuit interrupter 9 that are ongaged when this circuit interrupter is open, and the operating coil 59 of the tran; lay (it) across the bus section 5.

The contact members 92-3 of the load rclav 11 are adapted to be engaged when the total load demandon the translating device. and 2 has decreased to within the capacit of one translating devic t demand has decreased to sue difference in voltage of ti and 6 has decreased to such value that the contact members 92 of the ditierentia voltage 89 are ei'igaged, the operating coil 59 of the transfer relay G0 is energized. The relay ()0 thereupon effects engi z e cincut of its contact nien'ibcrs (i1, (52 and G and disengagenient of its contact members (i-land hi).

As has been previously described, the actuation of the relay to transfers the control of the reversible motor 38 from the voltage regulating device 37 to the voltagqje alancing device 6?. Since the o crating coil -18 of the transfer re ay l9 is not now encrgized. however, connection is mainlainml h. tween the bus section 5 and the operating coil 66 of the voltage balancing device (57. The voltage generated by the tiauislating tlcrice 2 is therefore regulated until the volage of the bus section (3 is made equal to that of the bus section 5, wlrcn it is permissib e to close the circuit interrupter 9 to connccl the two bus sections.

The circuit extending through the operating coil 74L of the time-delay relay 5 is now open. because the contact nicuiheuiii) of the transfer relay 49 are disengaged. but the operating coil 95 of a time-delay re ay 96 is adapted to be energized from the bus section 5 through the contact members Tl of the voltage balancing device (ST, contact members 56 of the transfer relay 5S that are engaged because the operating coil 48 of this relay is tie-energized, and contact members 61 of the transfer relay 69 that are now engaged.

The time-delay relay 96 is similar to the relay 75 in that its contact mcn'ihcrs 9i" and 98 are not energized as soon as the contact members 71 of the voltage balancing device 67, but only after the balanced condition has prevailed to maintain encrgization of the operating coil 95 for a predeterniin"l in tar-- val of time. hen this interv l elapsed, the contact members at. or the time-delay relay are engaged. Eng-ancment of the contact members 9? coni iietes a circuit extending from the bus section 5 to the operating coil 83 of the circu t inte rupter 9 through the resistor The circuit run, it.

()1,- interrupter 9 is thereupon closed to connect the bus sections 5 and (3 and to ct'z' ct en gagement of auxiliary contact members Fi lcontact members 94.

and 99-and disengagement of the auxiliary The contactmembers 84 so shunt the contact'membersQT of thetiine-dclay relay 96 as to maintain energization of the operating coil 83 0f the circuit intermipter 9 after the contact members 97* aredisengaged.

The auxiliary contact members99 of the circuit interrupter 9 co-operate withithe contactmembers 98 of the time-delayrelay 96 to short-circuit the operating coil 78 of the circuit interrupter 8. The circuit interrupter 8 is thereupoi'i'opened by the action of a compression spring 100 to disconnect the translating device *Zfrom the bus section 6.

When the auxiliary contact members 94 are disengaged because of closing of the circuit interrupter 9, the circuit extending through the operating coil 59 of" the transferrrelay is interrupted to permit this relay'to return to its deenergized-condition.

When the circuit interrupter Sisopened, its auxiliary contact members 82 are disengaged to disconnect one terminal of the armature member: of the reversible motor,38 from; one side of; the bus section 6. The motor 38is thereby rendered ineffective-to actuate! the contact arm 39' to vary the amount of the resistor 40 that isconnected invcircuitf with the shunt field-magnet winding. 41 of: the translating, device Inasmuch as the translating device 21s disconnected from thesystem, it is not. necessary that its voltage be subjected to the control of the motor 38' and the regulating device 37. The motor 38. remains ineffective until the transfer relay 49. effects engagement of its contact members52 as previously described.

The two bus-sections? 5and are now connected because the-clrcuit interrupter 9 is closed and the translating device 1.

alone supplying energy 1 to; both loadcircuit-s 3.21mi 4' because-the circuit interrupter 8 is opento disconnect the translating device 2 fromthe system. These conditions'are the same as those originally:described, and the apparatus'inuthe station" is in condition to I respondito the same conditions as previously desoribedto connect the translatingdevice 2 to the system and 'toithen disconnect the bus sections 5 andfi.

It will 5 be understood that the system embodying my inventionqis not limited to the specific'details of construction and connections that have shown inthe drawings and described in'the foregoing specification, as many, changes andmodifications may 1 be madetherein without departing from the spirit and scopeof my-invention, as setrforth infthe appended claims.

I' claimas my invention: J r I 1. In an electrical system, the combination withtwo bus sections, connecting means therebetween, a load circuit connected to each, bus 1 section, a supply- (illclllt for each bus section, and connecting means between each supply cn'cuit and the corresponding bus section, of means for maintaining the connectingmeans between the two bus sections and the connecting means between one or the supply circuits and the correspond the total power demand of'the two load circuits is below a predetermined value.

2. In an electrical system, the combination with two bus sections, connecting'means therebetween, a load circuit connected to each bus section, a supply circuit for. each bus section and connecting means between each supply circuit and the corresponding bus section, of means for maintaining the connecting meansbetween thet'wo bus sec,- tions ineffective and the connecting means between each of the supply circuits and the corresponding bus section effective while the difference in voltage of the two bus sections is above a predetermined value. 1

3. In an electrical system, the combination with two bus sections, connecting means therebetween, a load circuit connected. to each bus section, a supply circuit 'for'each bus section and connecting means between each supply circuit and the corresponding bus section, ot meansresponsive to the potentials of both bus sections for maintaining the connecting means between the twobus sections ineffective and the connectingmeans between each of the supply circuits and the corresponding bus section effective,

4. In an electricalsystem, the combination with two' bus sections, connecting means therebetweema load circuit connected; to each bussection, a supply circuit for each cuit and the corresponding bus section in response to predetermined conditions, means dependent upon said voltage equalization for renderin the connectin means between said last-named supplyeircuit and bustsection effective, and means dependent uponthe actuation of said connecting means for rendering the connecting; means between the t-wobus sections ineffect ve. a

5,. In an electrical system, the combination with two bus sections, connecting means therebetween, a, load circuit connected to each bus section, a supply circuit for each bussection and connecting means between-each supply circuit and the corresponding bus section, of means operative while the connecting means between the two bus sections and only one of the connecting means between the supply circuits and the respective bus sections are effective, for equalizing the voltages oi the disconnected supply circuit and the corresponding bus section when the voltage across one of the load circuits is below a predetermined value, means dependent upon said voltage equalization for rendering the connecting means between said last-named supply circuit and bus section effective. and means dependent upon the actuation of said connecting means for rendering the connecting means between the two bus sections inefi'ective.

6. In an electrical system, the combination with two bus sections, connecting means therebetween, a load circuit connected to each bus section, a supply circuit for each bus section, and connecting means between each supply circuit and the corresponding bus section, oi? means operative while the connecting means between the two bus sections and only one of the connecting means between the supply circuits and the respective bus sections are efiective, tor equalizing the voltages of the disconnected supply circuit and the corresponding bus section when the voltage across the load circuit that is connected to said last-named bus section is below a predetermined value, means dependent upon said voltage equalization for rendering the connecting means between said last-named supply circuit and bus section eiiective, and means dependent upon the actuation of said connecting means for rendering the connecting means between the two bus sections ineftective.

7. In an electrical system, the combination with two bus sections, connecting means therebctween, a load circuit connected to each bus section, a supply circuit for each bus section and connecting means between each supply circuit and the corresponding bus section, of means operative while the connecting means between the two bus sections and only one of the connecting means between the supply circuits and the respective bus sections are eliective, tor equalizing the voltages of the disconnected supply circuit and the corresponding bus section when the total power demand of the two load cir cuits is above a predetermined value, means dependent upon said voltage equalization for rendering the connecting means between said last-named supply circuit and bus section eil'ective, and means dependent upon the actuation of said connecting means for rendering the connecting means between the two bus sections ineffective.

S. In an electrical system, the combination with two bus sections, connecting means therebetween, a load circuit connected to each bus section, a supply circuit for each bus section, and connecting means between each supply circuit and the corresponding bus *tion, of means operative while the connecting means between the two bus sections are ineti'ective and the connecting means between each of the supply circuits and the corresponding bus sections are eli eclive for equalizing the voltages of the two bus sections in response to predetermined conditions, means dependent upon said voltage equalization for rendering the connect ing means between the two bus sections etl'ective, and means dependent upon the actuation of said connecting means for rendering the connecting means between one of the supply circuits and the corresponding bus section inetl'ective.

9. In an electrical system, the combination with two bus sections, connecting means lherebetween, a load circuit connected to each bus section, a supply circuit for each bus section and connecting means between each supply circuit and the corresponding bus section, of means operative while the connecting means between the two bus sec tions are ineffective and the connecting means between each of the supply circuits and the correspondin bus sections are effective, for equalizing tie voltages of the two bus sections when the difference in voltage oi the two bus sections is below a predetermined value and the total power demand of the two load circuits is below a predetcrmined value, means dependent upon said voltage equalization for rendering the connecting means between the two bus sections cliective, and means dependent upon the actuation of said connecting means for rcn dering the connecting means between one of the supply circuits and the corresponding bus section ineliective.

10. In an electrical system, the combination with two bus sections, connecting means thcrebetween, a load circuit connected to each bus section, a supply circuit for each bus section and connecting means between each supply circuit and the corresponding bus section, of means responsive to the potential of both bus sections and co-operating means responsive to the currents traversing both supply circuits for maintaining the connecting means between the two bus sections inettective and the connecting means between each of the supply circuits and the corresponding bus sections efifective.

11.. In an electrical system, the combination with two bus sections, connecting means therebetween, a load circuitconnected to each bus section, a supply circuit for eacl bus section and connecting means between each supply circuit and the corresponding bus section, of means responsive to the difierence in potential of the two bus sections and co-operating means responsive to the sum of the currents traversing the two supion eii'ective and the connecting means between each of the supply circuits and the corresponding bus section effective.

12. In an electrical system, the combination with two bus sections, connecting means therebetween, a load circuit connected to each bus section, a supply circuit for each bus section and connecting means between each supply circuit and the corresponding bus section, of a differential relay device energized in accordance with the potentials of both bus sections and a co-operating suminating relay device energized in accordance with the currents traversing both supply circuits for maintaining the connectingmeans between the two bus sections ineffective and the connecting means between each of the supply circuits and the corresponding bus section efi'ective.

13. In an electrical system,,the combination' with two bus sections, connecting .means therebetween, a load circuit connected to each bus section, a supply circuit for each bus section and connecting means between each supply circuit and the corresponding bus section, of means for maintaining the connecting means between the two bus sections ineffective and the connecting means between each of the supply circuits and the corresponding bus section effective while the difference in voltage of the two bus sections is above a predetermined value, and means for maintaining the voltage of each of the load circuits substantially constant at a respectively predetermined value.

In testimony whereof, I have hereunto subscribed my name this 27th day of March, 1924. I

CHARLES E. CAREY. 

